The recent introduction of endoluminal graft prostheses, such as stents and stent-graft systems, for the treatment of arterial and venous defects, such as aneurysms, hold the promise of reduced procedural morbidity and mortality compared to previously known surgical alternatives.
For example, U.S. Pat. No. 5,078,726 to Kreamer describes a stent graft system wherein a graft is affixed to intact portions of a vessel above and below an aneurysm using coiled sheet stents. Likewise, U.S. Pat. No. 5,219,355 to Parodi et al. shows a graft affixed to intact portions of a vessel wall above and below an aneurysm using balloon-expandable stents. U.S. Pat. No. 5,275,622 to Lazarus also shows a graft affixed at its upper and lower ends using self-expanding sinusoidal rings.
One drawback encountered with systems such as those described in the foregoing patents is that relative movement of the upper and lower fixation devices after initial deployment of the stents may result in twisting of the graft material. Such torsional displacements between the ends of the graft may cause a reduction in the flow area of the graft and/or the creation of stagnation zones that promote clotting within the lumen of the graft.
In addition, excluding an aneurysm from the flow path and subsequent clotting of the blood contained within the aneurysmal cavity may result in foreshortening of the vessel, thereby causing longitudinal movement of the graft fixation devices towards one another. Such longitudinal displacements may in turn cause buckling: the graft may bow outward, sag, kink, or crumple, again promoting stagnation zones and thrombus formation within the lumen of the graft.
Moreover, because the structure of the human vascular tree varies from patient to patient, each procedure is a unique experience. For example, an aneurysm existing in a straight vessel segment may be excluded with a tubular graft, whereas an aneurysm occurring at, abutting or including a vessel bifurcation may require the use of a custom prosthesis.
Repair of an aneurysm located adjacent to a bifurcated vessel presents further technical difficulties, including the inability to easily enter both vessel branches because of vessel size, vessel tortuosity, device size, or limited device flexibility. There may also be an inability to adequately expand the device and create fluid seals at the ends of the aneurysm. If a custom device does not fit, surgical intervention also may be necessary to remove the device, thereby exposing the patient to additional risk. These problems are compounded where the diseased area of a vessel may change in length, size, and shape after the prosthesis has been deployed.
In view of the foregoing, it would be desirable to provide a vascular prosthesis that may be readily adapted to vessels of various sizes, including bifurcated vessels.
It further would be desirable to provide a vascular prosthesis that can accommodate changes in the size and shape of the vessel after the prosthesis has been deployed.
It also would be desirable to provide a vascular prosthesis that can accommodate torsional and longitudinal displacements between the fixation devices that affix the vascular prosthesis to intact portions of the vessel wall, without twisting or kinking of the prosthesis.